Vacuum processing chambers are generally used for chemical vapor depositing (CVD) and etching of materials on substrates by supplying process gas to the vacuum chamber and application of an RF field to the gas. Examples of parallel plate, transformer coupled plasma (TCP.TM., also called ICP), and electron-cyclotron resonance (ECR) reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; and 5,200,232. The substrates are held in place within the vacuum chamber during processing by substrate holders. Conventional substrate holders include mechanical clamps and electrostatic clamps (ESC). Examples of mechanical clamps and ESC substrate holders are provided in commonly owned U.S. Pat. No. 5,262,029 and commonly owned U.S. application Ser. No. 08/401,524 filed on Mar. 10, 1995. Substrate holders in the form of an electrode can supply radiofrequency (RF) power into the chamber, as disclosed in U.S. Pat. No. 4,579,618.
Plasma reactors wherein an antenna coupled to a radiofrequency (RF) source energizes gas into a plasma state within a process chamber are disclosed in U.S. Pat. Nos. 4,948,458; 5,198,718; 5,241,245; 5,304,279; 5,401,350; 5,531,834; 5,464,476; 5,525,159; 5,529,657; and 5,580,385. In such systems, the antenna is separated from the interior of the process chamber by a dielectric member such as a dielectric window, gas distribution plate, encapsulating layer of epoxy, or the like, and the RF energy is supplied into the chamber through the dielectric member. Such processing systems can be used for a variety of semiconductor processing applications such as etching, deposition, resist stripping, etc.
During an oxide etch of a semiconductor wafer in a plasma reactor, polymer can build up on the exposed surface of the dielectric member. As the polymer build-up deepens the uniformity of processing of the substrate can be affected and/or polymer can then flake off of the dielectric member. If the dielectric member is located directly above the substrate and chuck, polymer particles can fall directly on the substrate or the chuck below. This can ruin the substrate decreasing yield or cause chucking problems. In addition, the process must be stopped and the chamber cleaned. The delay due to the "down-time" required for cleaning also represents a substantial loss in production yield. Therefore, control of the deposition of polymer on the dielectric member is critical for achieving a high yield and maintaining through-put of the substrates in the plasma reactor.